Quartz lamp seal

ABSTRACT

An electric lamp including an envelope of quartz glass in which at least part of the metal components sealed in the pinch is coated with SiO2.

Unlted States Patent 1 1 1111 3,753,026 Goorissen Aug. 14, 1973 [54] QUARTZ LAMP SEAL 3,617,797 11/1971 M61 31 6131. 313 318 2,992,959 7/1961 Schr'ewelius 338/330 .1 r fi JEHQQQK QQ1 QW Q$ 3,681,737 8/1972 Magnusson 61 a]. 338/330 Emdhoven, Netherlands 3,105,867 10/1963 M61161 174/5064 3,669,693 6/1972 DallOl'l 61 8|. 117/201 [73] Assgnee' g'fi New York 3,549,933 12/1970 Smalley 313/318 x 2,113,984 4/1938 116111161 61.... 174150.64 x 3,515,420 6/1970 Thomasson B! 811 174150.64 x [221 #1970 3,211,826 10/1965 Holcomb 6131. 313/318 ux [21] Appl. N6.: 95,436

Primary Examiner-Rudolph V. Rolinec [30] Foreign Appuumon Priority Data Assistant Examiner--Marvin Nussbaum D66. 13, 1969 Netherlands 6918746 Tnfan [52] US. Cl. 313/318, 313/332 S R llil- H01! 9 H011 5/46, H011 An electric lamp including an envelope of quartz glass [58] Field of Search 313/315, 317, 318, in which at least part of the metal components sealed 313/332; 174/ in the pinch is coated with SiOz.

[ 5 References Cited 4 01111118, 5 Drawing Figures UNITED STATES PATENTS 3,420,944 1/1969 HOlCOmb 174/5064 PAIENTEBnuc 14 ms INVENTOR. JAN GOORISSEN QUARTZ LAMP SEAL The invention relates to an electric lamp including an envelope of quartz glass or a similar high melting-point material which is transparent to light and has a low thermal coefficient of expansion, which lamp includes at least one pinch in which at least one strip consisting of a metal foil is sealed in, at least one current conductor of metal wire being secured by means of welding to both ends of said strip, while one conductor serves as an electric contact for the lamp. The foil consists of a metal having a melting point of more than l,500C so that during sealing in the foil cannot melt. For this use a metal is chosen having a low thermal coefficient of expansion. Usually the foil consists of tungsten, molybdenum or a suitable alloy of tungsten and molybdenum.

In lamps of this kind a strip in the form of foil of such a metal is used in the pinch because it has been found that in spite of the difference in coefficient of expansion between quartz glass on the one hand and the metal on the other hand a gastight closure can be obtained therewith.

The construction of the pinch in question is frequently used in high-power lamps such as infrared radiators and halogen lamps in which not only the envelope but also the pinches may assume a high temperature when the lamps are operating.

During the manufacture of the pinch a capillary space is substantially always formed around that part of the current conductor partially extending beyond the lamp which is present within the pinch.

In high-power lamps the pinch often cracks during use. This is generally ascribed to an oxidation of the current conductor partially extending beyond the lamp and of the metal foil strip. This oxidation is caused by oxygen and water vapour from the air which may reach the foil through the capillary along this conductor.

Various steps have been proposed to protect the portion of the conductor extending beyond the lamp and being present within the pinch and the metal foil strip against oxidation. The object of the proposed steps is either to enhance the adhesion between quartz and the metal parts or to provide the metal parts with an oxidation-protective layer. The materials used for this purpose are metals or metal oxides which cannot be oxidized at the temperature of the pinch. In practice these steps were not found to be successful because it was still difficult to obtain a permanently gastight closure when using these materials.

An object of the present invention is to provide an electric lamp in which cracking of the pinch as a result of oxidation of metal parts in the pinch does not occur or substantially does not occur.

It was found that this may be achieved with a lamp which is characterized in that at least the part located within the pinch of the current conductor partially protruding from the lamp, the area where this conductor is secured to the metal foil strip and at least the part of this strip adjacent to the area of securement are coated with a thin film of SiO,.

For achieving the desired effect an SiO, film having a thickness of from 0.5 pm to 2 pm is found to be In order that the invention may be readily carried into effect some embodiments thereof will nowbe described in detail by way of example with reference to the accompanying diagrammatic drawing in which FIG. 1 shows a molybdenum strip including current conductors, which strip is partially coated with SiO FIG. 2 is a cross-section taken on the line II--Il of FIG. 1.

FIG. 3 shows a molybdenum strip including current conductors, which strip is completely coated with SiO FIG. 4 is a cross-section taken on the line IV-IV of FIG. 3 according to the invention.

FIG. 5 shows a cross-section of part of a halogen lamp.

FIG. 1 shows in a plan view a molybdenum strip 1 to which a molybdenum current conductor 2 and the end of the filament 3 are secured by means of welding. Part of the current conductor 2 and part of the molybdenum strip 1 are coatedwith a thin film 4 of SiO, which is obtained by sputtering.

FIG. 2 shows in a side elevational view a crosssection taken on the line II-II of FIG. 1. The thickness of the film 4 is approximately 1 pm. This construction .is used if after providing the SiQ, film something else is to be secured to the molybdenum strip by means of welding.

FIG. 3 shows in a plan view a molybdenum strip 5 to which two current conductors 6 and 7 are secured by means of welding. Part of the conductors 6 and 7 and the strip 5 are coated with a thin film of SiO (8) which is provided by means of sputtering. After the strip 5 and the conductors 6 and 7 welded thereto are coated with Si(), the filament 9 is secured to the conductor 8.

FIG. 4 shows a cross-section taken on the line IV-IV of FIG. 3.

The thickness of the SiO, film is in this case likewise approximately 1pm. The SiO, films were obtained by means of sputtering in an argon atmosphere at a pressure of approximately 2 X 10 Torr. The rate of application was approximately 250 A per minute. A voltage of several kV was applied with the aid of a highfrequency generator l kw, frequency 20 MC) between the cathode and the substrate to be coated. The parts of the molybdenum strip and the conductors secured thereto which were not to be coated with SiO, were covered with a mask.

FIG. 5 shows in a cross-section a part of a halogen lamp (1,000 W, Volts) whose pinch temperature during operation of the lamp may increase to approximately 400C in certain types of reflectors. The thickness of the molybdenum foil 10 is approximately 35am. A thin film 11 of SiO, (approximately lum thick) is provided on the molybdenum foil, which film also extends beyond the pinch over approximately 5 mms on the molybdenum conductor 12. The lamp includes a spiral 13 in an atmosphere consisting of argon and a small quantity of iodine (total pressure 2.5 atmospheres). The lifetime of this lamp is approximately 2,000 hours.

Number of lumens/Watt: 22. If there is no SiO film oxidation in the pinch 14 occurs already after ashort period in many cases followed by cracking of the pinch. When using the film of SiO, no oxidation in the pinch of the molybdenum parts can be found, noteven at the end of the lifetime of the lamp.

What is claimed is:

1. In an electric lamp of the type having an envelope within the pinch, the area where this conductor is seof a high melting-point material such as quartz glass, cured to the metal foil strip, and the part of this strip which is transparent to light and has a low thermal coadjacent the area of securement.

efficient of expansion, which lamp includes at least one 2. An electric lamp as claimed in claim. 1, wherein the pinch in which at least one strip consisting of a metal 5 thickness of the SiO, film is between 0.5 and 2 pm; foil is sealed in, at least one current conductor of metal 3. An electric lamp as claimed in claim 1, wherein wire being secured by means of welding to each end of said metal foil is molybdenum.

said strip, one conductor serving as an electric contact 4. The lamp as claimed in claim 1 wherein said thin for the lamp wherein the improvement comprises that film of SiO forms a coating over the entire metal foil a thin film of SiO, forms a coating over the portion of 1() strip and the ends of the conductors. the contact serving current conductor which is located 

2. An electric lamp as claimed in claim 1, wherein the thickness of the SiO2 film is between 0.5 and 2 Mu m.
 3. An electric lamp as claimed in claim 1, wherein said metal foil is molybdenum.
 4. The lamp as claimed in claim 1 wherein said thin film of SiO2 forms a coating over the entire metal foil strip and the ends of the conductors. 